A cutting tool of a cubic boron nitride sintered body having a cutting edge prepared by sintering fine cubic boron nitride powder with a binder exhibits excellent performance with respect to cutting of a hard iron group or cast iron.
Following automation of a machine tool or introduction of unmanned operation into a production process, improvement of chip treatability has recently been required as an item necessary and essential for continuous running along with long-livedness of a cutting tool. However, a conventional cutting tool of a cubic boron nitride sintered body is hardly provided with a chip breaker for parting chips, and hence abnormal detachment of a work or the tool or deterioration of the work surface so easily results from involution of chips during automatic operation of a machine tool that the automatic operation may be rendered impossible to inhibit improvement of productivity.
On the other hand, each of Japanese Patent Laying-Open Nos. 8-155702, 4-217404 to 4-217409 and 8-52605 discloses a cutting tool of a hard sintered body having a chip breaker. The cutting tool described in this literature is provided with a single- or multi-start linear breaker shape for spirally curling chips due to this shape and enabling chip treatment.
However, the cutting tool provided with the chip breaker having such a simple shape disadvantageously requires a tool provided with different right and left hands depending on tooling, a tool provided with a breaker suitable to each of outer diameter working and end face working, a tool provided with a breaker corresponding to each of cutting conditions having different feed rates or depths of cut.
Particularly in working (carburized layer removal) for cutting hardened steel by about 0.3 to 0.7 mm at a time for removing a carburized layer, hardness of the work remarkably varies with the depth of cut, to result in variation in chip outflow direction and chip treatability. This carburized layer removal requires a tool provided with a breaker responsive to the hardness of the work. In other words, the conventional tool provided with a breaker attains the effect of chip treatment only under specific cutting conditions and is unapplicable to wide-ranging working conditions, and hence a plurality of tools are disadvantageously required in response to various tooling conditions.
In the cutting tool described in each of Japanese Patent Laying-Open Nos. 4-217404 to 4-217409, the surface roughness of the upper surface of the superhard sintered body having the chip breaker is set to at least 0.5 S and not more than 10 S or the like, in order to easily curl chips. When the cutting tool is employed for cutting a hard work such as hardened steel in particular, however, chips are so hard that frictional resistance is increased due to the chips and a rake face of the tool is easily damaged by heat resulting from rubbing if the surface roughness of the superhard sintered body is in excess of 0.5 S. Consequently, the shape of the tool is disadvantageously changed due to progress of crater wear, to reduce the chip treatability.
Japanese Patent Laying-Open No. 8-52605 discloses a cutting tool provided with a chip breaker and a rake face having a cutting face formed at a positive shear angle. In this cutting tool, however, the strength of a cutting edge is so insufficient for stable cutting that an edge frequently causes tool failure during cutting when the cutting tool is employed for cutting a hard work such as hardened steel.
Patent Literature 1: Japanese Patent Laying-Open No. 8-155702
Patent Literature 2: Japanese Patent Laying-Open No. 4-217404
Patent Literature 3: Japanese Patent Laying-Open No. 4-217405
Patent Literature 4: Japanese Patent Laying-Open No. 4-217406
Patent Literature 5: Japanese Patent Laying-Open No. 4-217407
Patent Literature 6: Japanese Patent Laying-Open No. 4-217408
Patent Literature 7: Japanese Patent Laying-Open No. 4-217409
Patent Literature 8: Japanese Patent Laying-Open No. 8-52605